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| Book/Report | FZJ-2016-06610 |
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1988
Kernforschungsanlage Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/12975
Report No.: Juel-Spez-0487
Abstract: This report contains all the details of the results presented in Jul-2234 (or the German original Jul-2091) on fission product release from spherical fuel elements during accident condition testing. In addition, release results from new tests and the results from the extensive post-irradiation examination work on heated fuel elements are presented. The conclusions obtained in Jül-2234 are being affirmed and extended. At 1600 °C, fission product release from spherical fuel elements is limited to the contribution of the contamination, since the particles remain intact. An exception to this is Ag 110m. At 1800 °C, deterioration of the SiC layer can be observed to various degrees leading to cesium release from individual coated particles and the buildup of cesium in the matrix graphite of the fuel element. Release from the sphere is observed only after some delay. Strontium is still strongly retained in fuel kernels and in the matrix graphite. Largest release fractions are observed with silver which diffuses fast through matrix graphite. Starting at 1800 °C, and increasing with higher temperatures, release of fission gases and iodine is getting larger due to occasional pressure induced particle failures and due to SiC corrosion and thermal decomposition. Gas release levels can reach 0.1 % after heatup to 1800 °C and 14 % after heatup to 2500 °C. Under these heating conditions, cesium release is 1 - 6 %, and 100 %, respectively. The most important conclusion is that the release of all safety relevant radionuclides is negligible for temperatures up to 1600 °C and heating times up to 500 hours. At 1700 °C and 1800 °C, fission product retention in fuel elements with TRISO particles is strongly dependent on the heating time and also on the prior irradiation conditions.
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